Grade 5: 12 & 24 Hour Time

Warm up with a quick recall on the board. Line up 12- and 24-hour time: after midday, add 12 to the hour (1 pm = 13:00); midnight is 00:00, midday is 12:00. Practise converting both directions.

The 24-hour clock counts the hours straight through from 00:00 to 23:59, so there is no am or pm and no repeating numbers. It is used on timetables, computers and in the military. Converting to and from 12-hour time comes down to the afternoon rule: after midday, add 12 to the hour. Model the method clearly, thinking aloud:

• Show why it exists: 3 o'clock is ambiguous, but 03:00 and 15:00 are not, which is why timetables use it.
• Teach that morning hours match (9 am is 09:00) and always use two digits for the hour.
• Teach the afternoon rule: from 1 pm onwards, add 12 to the hour (2 pm is 14:00, 8 pm is 20:00).
• Handle the two tricky boundaries: midnight is 00:00 and midday is 12:00.
• Practise both directions with real timetables, and work out durations in 24-hour time.

Work this through step by step on the board, then have the class talk you through a second one.

• Write 2:45 pm in 24-hour time:
• afternoon, so add 12 to the hour
• 2 + 12 = 14
• 2:45 pm = 14:45

Do the first few questions of the practice worksheet together, one child explaining each step. Check for understanding before releasing the class to work alone.

Students complete the worksheet independently. Hand out the three difficulty levels below so every child works at the right stretch.

Circulate and look for these, they are the usual sticking points:

• Adding 12 to morning times as well as afternoon ones.
• Getting midnight and midday the wrong way round (midday is 12:00, midnight is 00:00).
• Writing a pm time without adding 12 (13:00 written as 1:00).
• Adding 12 to the minutes instead of the hour.
• Adding 12 to morning (am) times, and mishandling 12 am (→ 00:00) and 12 pm (stays 12:00).

Pull the class back together. Ask one child to explain 12 & 24 hour time in their own words, pose a single check question everyone answers on a mini whiteboard, and name what you will build on next lesson.

Use the independent worksheet as the evidence. A child who can complete it accurately and explain one answer has met the objective; anyone who cannot needs the easier level and a short reteach next session.